Reserve batteries represent reliable sources of portable electrical power following long periods of storage and are designed to be activated very quickly with little degradation in performance over time. In some applications, the reserve battery must have a prolonged shelf life even at extreme temperatures. Once activated, the reserve battery electrically powers a circuit for a few seconds to a few minutes. No maintenance is required for the reserve battery during storage prior to use, permitting it to be permanently installed in equipment.
One reserve battery construction, widely used as a source of in-flight electrical power for components of artillery projectiles, physically separates a reservoir filled with electrolyte and cell electrodes with a frangible barrier. The battery cells are stored in a dry condition and are wetted during flight of the projectile with electrolyte. In artillery projectiles, the reserve battery should have a shelf life exceeding twenty years while stored at temperatures ranging from −40° F. to +145° F. When the artillery shell is loaded into a weapon and the weapon is fired, the set back force applied by the artillery projectile to the reserve battery precipitates rupture of the frangible barrier.
Electrolyte flows from the reservoir through the breach in the frangible barrier and wets the cell electrodes, which activates the reserve battery for powering a circuit in the artillery projectile such as electronics of a proximity fuse or electronics of a self-destruct mechanism.
Conventional reserve batteries include, as distinct components, a fill port and a breaking device. The fill port is used to introduce electrolyte into the reservoir inside the reserve battery and may be sealed using a ball seal with an interference fit.
The breaking device operates to rupture the frangible barrier when the weapon is fired, so that the electrolyte can wet the cell electrodes. In small conventional reserve batteries, the fill port and the breaking device collectively occupy a significant volume of the reservoir that could otherwise be used to store electrolyte, which represents a significant disadvantage.
It would be desirable, therefore, to provide a compact reserve battery with improved space utilization.